Field of the Invention
The present invention relates to a sensor equipped wheel support bearing assembly having a load detecting sensor built therein for detecting a load imposed on a bearing of a wheel.
Description of Related Art
As a technique to detect a load imposed on each of wheels of an automotive vehicle, such a wheel support bearing assembly has been made in which a strain gauge is pasted to an outer ring of the wheel support bearing assembly so that the load can be detected from a strain in an outer ring of an outer diametric surface. In this respect, see, for example, the patent document 1 listed below. It has, however, been found that the wheel support bearing assembly disclosed in the patent document 1 is incapable of detecting the load accurately since, when the load acting on the wheel support bearing assembly is to be detected, the amount of deformation of a stationary ring relative to the load is so small as to result in a small amount of strain and, therefore, the detecting density is lowered enough to fail to detect the load accurately.
In order to resolve the problems referred to above, such a sensor equipped wheel support bearing assembly, which is constructed as subsequently discussed, has been suggested. In this respect, see the patent document 2 also listed below. The sensor equipped wheel support bearing assembly disclosed therein includes an outer member having an inner periphery formed with double rows of raceway surfaces, an inner member having an outer periphery formed with raceway surfaces in face to face relation with the above described raceway surfaces in the outer member, and double rows of rolling elements intervened between the respective raceway surfaces of the outer and inner members that are held in face to face relation with each other, which assembly is used to rotatably support each of the wheels relative to a vehicle body structure. An outer diametric surface of a stationary member, which is one of the outer and inner members, is provided with at least one pair of a sensor unit pair comprised of two sensor units disposed at respective circumferential portions of the stationary member and spaced a 180° phase difference from each other in a circumferential direction thereof. Each of the sensor units referred to above includes a strain generating member, which has two or more contact fixing segments that are fixed to the outer diametric surface of the stationary member in contact therewith, and a sensor fitted to the strain generating member for detecting the strain induced in the strain generating member.
In the construction described above, on the basis of the difference between respective sensor output signals fed from the two sensor units in the sensor unit pair, a radially acting load acting on the wheel support bearing assembly in a radial direction is estimated by a radially acting load estimating unit. Also, on the basis of the sum of the sensor output signals of the two sensor units in the sensor unit pair, an axially acting load acting on the wheel support bearing assembly in an axial direction is estimated by an axially acting load estimating unit. The two sensor units of at least one pair of the sensor unit pairs are disposed at an upper surface area and a lower surface area of the outer diametric surface of the stationary member, which correspond respect to top and bottom positions, respectively, relative to a tire tread surface. On the basis of an output signal amplitude of the sensors of the sensor unit pairs, the direction of the above described axially acting load is determined by an axially acting load direction determining unit. The load estimating process in this case is shown in a schematic block diagram in FIG. 26 of the accompanying drawings attached to this specification.
If the contact fixing segments of the strain generating member in the sensor unit are disposed in the vicinity of the rolling surface of the stationary member, the sensor output signal accompanies a fluctuation proximate to the sinusoidal wave, as shown in FIG. 27, incident to rotation of the wheel. This means that a change in strain resulting from the passage of the rolling elements is detected. With the above described construction, since from the difference of amplitude values (vibration components resulting from a revolving movement of the rolling elements) in the sensor output signals of the two sensor units that are disposed respectively at the top and bottom positions, the axially acting load is determined and, in dependence on positive or negative of the axially acting load, the load is calculated with the use of a load estimating parameter appropriate thereto, the load can be estimated with a high sensitivity.